Skyline Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyline Observatory clear sky chart from 2005-11-05 to 2017-09-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
50%
15299
23%
46969
18%
15257
56%
15257
28%
28730

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
26%
719
23%
2327
10%
716
41%
716
19%
1507
January16th to endNight
29%
768
23%
2376
12%
768
40%
768
21%
1551
February1st to 15thNight
31%
704
22%
2112
10%
701
42%
701
24%
1330
February16th to endNight
29%
631
23%
1893
12%
631
37%
631
21%
1231
March1st to 15thNight
33%
720
20%
2136
12%
720
39%
720
22%
1412
March16th to endNight
38%
738
20%
2082
13%
738
44%
738
27%
1322
April1st to 15thNight
44%
539
25%
1797
17%
539
54%
539
32%
983
April16th to endNight
51%
540
27%
1771
21%
540
61%
540
32%
982
May1st to 15thNight
53%
540
21%
1620
14%
540
60%
540
31%
1006
May16th to endNight
68%
561
21%
1682
17%
561
71%
561
35%
990
June1st to 15thNight
70%
540
19%
1620
15%
540
73%
540
36%
940
June16th to endNight
78%
540
20%
1620
18%
540
79%
540
39%
913
July1st to 15thNight
71%
510
15%
1530
13%
510
72%
510
31%
953
July16th to endNight
75%
564
19%
1595
17%
531
77%
531
35%
948
August1st to 15thNight
75%
539
19%
1741
21%
536
76%
536
33%
1014
August16th to endNight
69%
573
21%
1910
24%
573
70%
573
27%
1194
September1st to 15thNight
66%
632
20%
1892
19%
632
68%
632
30%
1198
September16th to endNight
62%
669
29%
1848
23%
669
65%
669
35%
1108
October1st to 15thNight
58%
660
35%
1815
28%
660
63%
660
38%
1062
October16th to endNight
51%
704
32%
2150
28%
704
59%
704
34%
1224
November1st to 15thNight
50%
700
29%
2276
26%
700
59%
700
33%
1261
November16th to endNight
40%
720
28%
2340
20%
720
52%
720
27%
1398
December1st to 15thNight
36%
720
22%
2340
16%
720
46%
720
22%
1494
December16th to endNight
32%
768
20%
2496
15%
768
40%
768
18%
1709

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
14%5%25%5%35%45%7%39%
47818
Night
13%5%2442445%7%44%
47168
TransparencyDay
42%411%21%16%3
47519
Night
37%411%21%19%5%
46971
SeeingDay
17%6%17%22%22%13%
5198
Night
16%8%18%29%23%4
15302

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
22%7%24424345%38%
1611
16th to endDay
19%5%2442443444%
1845
February1st to 15thDay
17%10%35%314346%39%
1750
16th to endDay
18%7%26%5%34335%38%
1580
March1st to 15thDay
19%8%35%423446%36%
1824
16th to endDay
16%6%35%425%45%7%37%
2150
April1st to 15thDay
14%6%25%32445%7%42%
2151
16th to endDay
12%6%25%5%3445%7%42%
2187
May1st to 15thDay
14%7%25%5%3435%7%40%
2331
16th to endDay
12%5%35%5%46%5%5%9%37%
2431
June1st to 15thDay
8%426%5%5%6%7%7%10%35%
2340
16th to endDay
5%3147%36%6%7%10%41%
2340
July1st to 15thDay
10%5%36%7%48%7%8%9%30%
2340
16th to endDay
7%435%8%5%8%8%7%10%30%
2465
August1st to 15thDay
8%426%7%5%7%7%7%10%33%
2205
16th to endDay
13%5%26%7%5%7%6%6%8%29%
2292
September1st to 15thDay
13%5%26%6%35%6%7%8%34%
2055
16th to endDay
13%5%25%5%235%47%43%
1837
October1st to 15thDay
11%414433236%53%
1815
16th to endDay
12%5%2332324454%
1719
November1st to 15thDay
13%5%1332424454%
1582
16th to endDay
19%414313346%46%
1620
December1st to 15thDay
20%6%35%434445%36%
1620
16th to endDay
25%8%34432245%34%
1728
January1st to 15thNight
20%5%25%433336%40%
2327
16th to endNight
17%7%35%434435%40%
2376
February1st to 15thNight
17%7%24423246%43%
2103
16th to endNight
18%6%35%4245%45%40%
1893
March1st to 15thNight
17%6%24434447%39%
2136
16th to endNight
13%6%35%424446%44%
2082
April1st to 15thNight
13%31242445%8%49%
1797
16th to endNight
10%423424347%51%
1771
May1st to 15thNight
11%5%145%25%45%7%46%
1619
16th to endNight
6%324435%5%7%9%46%
1682
June1st to 15thNight
6%2145%25%7%6%11%46%
1620
16th to endNight
3323426%6%6%11%49%
1620
July1st to 15thNight
8%4245%46%6%7%10%40%
1620
16th to endNight
43245%27%6%7%13%40%
1703
August1st to 15thNight
5%3246%35%6%7%12%42%
1752
16th to endNight
9%426%5%35%5%6%9%40%
1910
September1st to 15thNight
9%5%25%6%35%5%6%7%43%
1892
16th to endNight
9%415%5%2445%7%49%
1848
October1st to 15thNight
10%424422346%55%
1815
16th to endNight
14%41431223456%
2150
November1st to 15thNight
13%423223346%53%
2276
16th to endNight
16%5%25%313345%48%
2340
December1st to 15thNight
17%5%25%434347%40%
2340
16th to endNight
23%7%35%3235%45%34%
2496

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
49%26%17%20%3
1612
16th to endDay
43%27%23%18%3
1845
February1st to 15thDay
46%27%21%18%3
1752
16th to endDay
49%17%20%17%3
1580
March1st to 15thDay
48%38%17%17%5%
1824
16th to endDay
43%414%21%13%1
2151
April1st to 15thDay
40%310%22%18%5%
2151
16th to endDay
39%39%25%17%3
2187
May1st to 15thDay
43%411%23%14%3
2331
16th to endDay
42%413%25%12%1
2435
June1st to 15thDay
39%6%16%22%13%
2340
16th to endDay
34%6%15%23%16%3
2340
July1st to 15thDay
43%7%15%20%9%3
2201
16th to endDay
42%8%18%21%8%
2310
August1st to 15thDay
41%8%15%19%13%1
2192
16th to endDay
47%7%12%19%10%2
2292
September1st to 15thDay
43%6%14%18%12%4
2055
16th to endDay
39%410%19%22%4
1837
October1st to 15thDay
34%36%19%27%8%
1815
16th to endDay
33%2420%29%9%
1719
November1st to 15thDay
34%25%19%29%8%
1582
16th to endDay
39%16%21%26%5%
1620
December1st to 15thDay
49%26%21%15%4
1620
16th to endDay
52%29%19%13%2
1728
January1st to 15thNight
46%27%20%19%3
2327
16th to endNight
46%27%19%18%5%
2376
February1st to 15thNight
43%18%21%19%5%
2112
16th to endNight
45%26%24%17%3
1893
March1st to 15thNight
44%38%18%17%6%
2136
16th to endNight
39%312%25%16%1
2082
April1st to 15thNight
32%213%24%20%6%
1797
16th to endNight
32%39%26%22%5%
1771
May1st to 15thNight
36%5%13%20%22%2
1620
16th to endNight
30%7%18%26%14%2
1684
June1st to 15thNight
29%6%18%28%14%1
1620
16th to endNight
26%7%18%24%19%4
1620
July1st to 15thNight
34%8%20%20%12%4
1530
16th to endNight
30%7%21%23%13%2
1595
August1st to 15thNight
31%7%19%22%15%2
1741
16th to endNight
38%6%16%23%12%2
1910
September1st to 15thNight
36%6%17%18%16%4
1892
16th to endNight
33%5%8%23%22%7%
1848
October1st to 15thNight
31%37%24%23%10%
1815
16th to endNight
33%2318%29%13%
2150
November1st to 15thNight
32%2421%26%12%
2276
16th to endNight
39%1419%26%7%
2340
December1st to 15thNight
44%28%19%19%5%
2340
16th to endNight
51%37%18%16%3
2496

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
32%16%30%14%6%
90
16th to endDay
25%25%37%8%4
96
February1st to 15thDay
26%28%36%6%1
90
16th to endDay
33%12%35%17%1
81
March1st to 15thDay
28%21%32%11%5%1
114
16th to endDay
24%9%29%21%13%2
288
April1st to 15thDay
20%9%22%28%15%2
270
16th to endDay
18%7%22%26%21%3
270
May1st to 15thDay
18%10%24%20%14%11%
288
16th to endDay
16%218%26%17%17%
331
June1st to 15thDay
11%48%23%27%24%
315
16th to endDay
9%312%21%26%26%
315
July1st to 15thDay
12%211%20%30%21%
305
16th to endDay
9%1320%34%29%
326
August1st to 15thDay
15%17%23%31%19%
313
16th to endDay
16%16%23%33%19%
332
September1st to 15thDay
15%411%16%32%20%
315
16th to endDay
19%38%22%36%8%
262
October1st to 15thDay
15%222%27%23%8%
255
16th to endDay
15%6%15%31%25%6%
176
November1st to 15thDay
26%12%23%27%7%2
90
16th to endDay
18%16%30%24%8%1
90
December1st to 15thDay
28%15%31%18%5%
90
16th to endDay
35%20%30%8%5%
96
January1st to 15thNight
26%15%26%23%7%
720
16th to endNight
22%14%29%30%3
768
February1st to 15thNight
22%12%28%32%4
704
16th to endNight
24%15%27%27%4
631
March1st to 15thNight
23%12%26%31%6%
720
16th to endNight
17%12%24%28%15%
738
April1st to 15thNight
16%9%25%30%16%1
539
16th to endNight
12%6%23%37%18%1
540
May1st to 15thNight
13%5%21%31%25%2
540
16th to endNight
8%210%34%38%5%
563
June1st to 15thNight
7%110%29%39%10%
540
16th to endNight
416%30%45%11%
540
July1st to 15thNight
9%16%27%40%14%
510
16th to endNight
6%1421%48%17%
564
August1st to 15thNight
8%424%49%13%
539
16th to endNight
11%25%24%46%9%
573
September1st to 15thNight
10%310%25%40%9%
632
16th to endNight
10%311%31%39%3
669
October1st to 15thNight
13%5%16%29%30%4
660
16th to endNight
16%8%17%30%24%2
704
November1st to 15thNight
15%9%20%29%21%3
700
16th to endNight
20%11%23%27%15%1
720
December1st to 15thNight
22%12%22%32%10%
720
16th to endNight
28%12%22%29%7%
768
Page generated at 2017-09-19 06:32:25. Version ac04

Copyright 2017 A. Danko


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